The invention relates to a method of activating safety device devices and, more particularly, to a method of operating safety devices such as air bags, belt tighteners, rollover bars, and the like.
Methods of this type are generally known and used in every vehicle. In many cases, an impact sensor is used, which is an acceleration sensor that preferably generates a signal representative of the forward movement or forward deceleration (displacement) of the vehicle. If this sensor signal exceeds a threshold value, a signal is generated which, at a minimum, prepares the activation of the safety device. This signal has to meet several conditions. Measured according to the total duration of a vehicle impact of, for example 30 ms, the signal has to be available at an early point in time. However, the signal also has to be unambiguous. Operating conditions of the vehicle must be unambiguously recognized which are only slightly different with respect to the sensor signal course from an actual impact, but in which the safety device should specifically not be triggered (no-fire situations). One example of such an operating condition that must be recognized is an extreme stressing of the vehicle. Such an extreme stressing may occur during a fast drive over a gravel and/or pothole plagued stretch of a roadway.
It is an object of the invention to provide a method of activating a safety device which, at an early point in time, supplies unambiguous information concerning the actual behavior of the vehicle and the resulting necessity of triggering the safety device or devices.
The invention achieves this object by providing a method of activating a safety device having a first impact sensor for generating a displacement signal reflecting the movement of the vehicle in a direction of displacement, and comprising a second impact sensor arranged away from the first impact sensor for generating a displacement signal reflecting the movement of the vehicle in the same direction of displacement. A processing device is provided by which the two movement signals, or signals derived therefrom, are correlated in a time-correct manner, wherein the safety device is activated according to predetermined correlations of the two signals.
The invention is characterized essentially by the following measures. Two impact sensors are evaluated. The evaluation takes place in an isochronous manner. The sensor signals are related to one another. This relationship of the signals is not rigid, but rather variable with respect to the time and the amount. By means of the amount, for example, the installation-site-caused variation of the reaction times of the sensors are taken into account as is the response behavior of the respective sensor, which is a function of the environment of the installation site and which, in comparison to the other sensor, may also be very different. A sensor which is disposed on a rigid engine mount generates a different signal signature than a sensor which experiences a crash event over a relatively soft “active path”.
In accordance with the invention, the sensor signals generated by different sensors are related to one another. “Different” may apply to the difference of the physical parameter (for example, acceleration and pressure) as well as to the mounting site, the response sensitivity, or also the response direction.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.